Narrow-ridged finless porpoise description

As its name suggests, the narrow-ridged finless porpoise (Neophocaena asiaorientalis) is a small marine mammal which lacks a dorsal fin(2), instead possessing a narrow, prominent ridge, which runs along the upper side of its relatively slender body (2)(3). The narrow-ridged finless porpoise is also distinguished by its rounded head, lacking an apparent beak (3), and its characteristic counter shading, with a dark to pale grey upper side, contrasting with a lighter grey underside (3). There is a scattering of horny tubercles on the dorsal ridge, which may create an anti-slip surface when the female carries its calf on its back. However, the tubercles also contain numerous nerve endings and are more likely used as sensory organs (3).

There are two recognised subspecies of narrow-ridged finless porpoise: the Yangtze finless porpoise (Neophocaena asiaorientalis asiaorientalis) and the East Asian finless porpoise (Neophocaena asiaorientalis sunameri). Both species are darker in colouration than the Indo-Pacific finless porpoise (Neophocaena phocaenoides phocaenoides) (3), which was previously recognised as the same biological species (1).

Related species

Narrow-ridged finless porpoise biology

The female narrow-ridged finless porpoise is thought to calve every two years, with the peak calving season varying with location. For the Yangtze finless porpoise this occurs in April and May, while in the East Asian finless porpoise population it occurs around May and June (3). It is estimated that the gestation period of species in the genusNeophocaena is around 11 months and the female feeds the calf for approximately 7 months. The narrow-ridged finless porpoise is known to reach sexual maturity at 4 to 9 years of age and lives for up to 25 years (3).

Narrow-ridged finless porpoise range

The two subspecies of the narrow-ridged finless porpoise each inhabit a slightly different range. The East Asian finless porpoise is found in the coastal waters around Taiwan, China, Japan, South Korea and possibly North Korea (1). The range of the Yangtze finless porpoise is isolated to the middle and lower reaches of the freshwater Yangtze River in China (1), including the adjoining lake systems (3)(4), where it is found up to 1,600 kilometres upstream (1).

Species with a similar range

Narrow-ridged finless porpoise habitat

The narrow-ridged finless porpoise favours shallow areas in close proximity to the shoreline. It is mainly found in coastal waters including shallow bays, mangrove swamps, estuaries and some large rivers, although it occasionally occurs in shallow water far from the shore. This species appears to have a strong preference for waters in areas with a sandy or soft bed (1). The Yangtze finless porpoise is the only subspecies to occur wholly in freshwater (2).

Narrow-ridged finless porpoise status

Narrow-ridged finless porpoise threats

The narrow-ridged finless porpoise’s preference for coastal and riverine habitats makes it highly vulnerable to the impacts of human activities that take place in these regions (3). Although the finless porpoise is not directly targeted by fishermen, large numbers die when they become entangled in fishing nets, particularly gillnets (3)(4). The deforestation of mangrove areas, rampant harbour expansion and the development of shrimp farms is taking place throughout Asia, further degrading the narrow-ridged finless porpoise’s coastal habitat (3)(4).

Electric fishing threatens of the Yangtze finless porpoise population; despite being illegal, this destructive fishing method is widespread in the river system, not only killing some individuals outright but also depleting their prey (4).The Yangtze finless porpoise is also particularly vulnerable to habitat degradation, with the river not only being impacted by fishing and pollution, but also by the numerous dams that dot the river basin (4). The impact that these threats may have on the Yangtze finless porpoise is illustrated only too well by the tragic demise of the baiji (Lipotes vexillifer), which is believed to have gone extinct from the Yangtze River in 2006 (5).

Furthermore, high levels of toxic pollutants have been reported to affect the Japanese population of East Asian finless porpoise, and while Neophocaena species tend to avoid boats (3), mortalities caused by collisions with vessels may be a problem in busy shipping areas (4).

Narrow-ridged finless porpoise conservation

The narrow-ridged finless porpoise is included on Appendix I of the Convention on International Trade in Endangered Species (CITES) under the original listing of Neophocaena phocaenoides(1)(7), as well as Appendix II of the Convention on Migratory Species (CMS) (8).

Since the 1980s, conservation measures have been proposed and implemented for the Yangtze finless porpoise (6). Preserving its natural habitat within the Yangtze River has been the principal concern and so by 2005, five natural reserves had been created in areas of the river that contain high numbers of the porpoise. In these reserves, the use of harmful fishing gear has been banned and these parts of the river are patrolled. However, these reserves are unable to eliminate all threats to the Yangtze finless porpoise and therefore ex situ conservation has also been undertaken (6).

The Baiji Dolphinarium was established in China in 1992, creating the opportunity to study endangered river animals in captivity. The Yangtze finless porpoise has been reared here for several years, with one giving birth in 2005; the first freshwater cetacean to have ever been born in captivity (6). Another small group inhabit a ‘semi-natural reserve’, which was initially created for the baiji (Lipotes vexillifer). While such efforts should be commended, not all have had particularly promising outcomes and the future of this species remains uncertain (4). More complete knowledge on this species is required as soon as possible to develop appropriate conservation measures for each subspecies(9).

Authentication

Glossary

A group of marine molluscs with grasping tentacles and either an internal or external shell. Includes squids, octopuses, cuttlefish and nautiloids.

Cetacean

A whale, dolphin or porpoise.

Cetaceans

A group comprising all whales, dolphins and porpoises.

Crustaceans

Diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Dorsal

Relating to the back or top side of an animal.

Dorsal fin

The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).

Ex-situ

Measures to conserve a species that occur outside of the natural range of the species. For example, in zoos or botanical gardens.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Gestation

The state of being pregnant; the period from conception to birth.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

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